Many sport-utility vehicles are equipped with a transfer case for transmitting drive torque to all four of the wheels, thereby establishing a four-wheel drive mode of operation. Some transfer cases are equipped with a mode shift mechanism which permits the vehicle operator to selectively shift between a two-wheel drive mode wherein only a primary (i.e., rear) driveline is driven and a “part-time” four-wheel drive mode wherein a secondary (i.e., front) driveline is rigidly coupled for rotation with the primary driveline.
In the past, the vehicle ride height and suspension configuration of many sport-utility vehicles provided sufficient packaging volume for a traditional transfer case having at least two rotating output shafts extending parallel to one another. In view of increased consumer demand for smaller four-wheel drive vehicles, the packaging volume allocated to the vehicle powertrain has been greatly reduced. While traditional transfer case designs may function in a satisfactory manner in certain vehicle applications, a need for an improved, compact, lightweight power transmission device exists.
In addition to such four-wheel drive vehicles, many all-wheel drive vehicles are now available which typically provide a two-wheel drive mode where the primary (i.e. front) driveline is driven and further provide an all-wheel drive mode where the secondary (i.e. rear) driveline is also driven. In most all-wheel drive vehicles, a power take-off unit is configured to transfer drive torque from the primary driveline to the secondary driveline via a transfer assembly and propshaft. Examples of single-speed and two-speed power take-off units and their arrangement in all-wheel drive vehicular applications are disclosed in commonly-owned U.S. Pat. Nos. 8,313,407 and 8,403,795.
Similarly to the packaging requirement of transfer cases in smaller 4WD vehicles, a need exists to provide compact power take-off units for use in smaller AWD vehicles.